TNF-α is a multifunctional immunomodulatory molecule in vivo that can work by binding to the cytomembrane receptor, which always causes target cell death (where its name is derived from) or induces local aggregation of immune effector cells. TNF-α is a soluble homologous trimeric subunit having a molecular weight of 17 KD (Smith, et al., J. Biol. Chem. 262:6951-6954, 1987). A transmembrane binding precursor of TNF-α with a molecular weight of 26 KD has also been found (Kriegler, et al., Cell 53:45-53, 1988). Mononuclear macrophages can secrete TNF-α and TNF-β when simulated with endotoxin and other stimulus, and some other cells can also secrete TNF-α.
TNF-α plays a crucial role in the pathological process of rheumatoid arthritis, bacterial or viral infection, chronic inflammation, autoimmune diseases such as AIDS, malignant tumors and/or neurodegenerative diseases. TNF-α monoclonal antibody can neutralize TNF-α and negatively regulate the activity of TNF-α in vivo. Moreover, a large number of studies have shown that TNF-α is the main medium which may cause septic shock syndrome. The increase of TNF-α level in blood serum of patients suffering from septic shock syndrome indicates the increase of mortality rate and disability rate. The clinical use of TNF-α antibody or its receptor has a certain therapeutic effect on septic shock syndrome.
In addition, TNF-α is one of the main media for promoting asymptomatic HIV infection status into AIDS, and monoclonal antibodies against TNF-α can neutralize the activity of TNF-α, negatively regulate the activity of TNF-α in vivo, and may remove the inducement from asymptomatic infection status into AIDS and achieve a certain purpose of AIDS treatment. Combined use of a TNF-α monoclonal antibody and other AIDS drugs counteracts the side effect due to excessive TNF-α and will distinctly enhance the therapeutic effect.
Initially, the scientists prepared and obtained murine anti-TNF-α monoclonal antibodies which were used to neutralize TNF-α. However, studies have shown that murine monoclonal antibodies have many disadvantages as drugs for treatment, because when used in the human body, the murine monoclonal antibodies have strong immunogenicity and fast elimination in vivo with a short half life, leading to limited clinical efficacy and considerable side effects. With the development of humanized monoclonal antibody technology, the disadvantages of the anti-TNF-α murine monoclonal antibody have been overcome. Thereamong, a human-mouse chimeric anti-TNF-α monoclonal antibody, Infliximab (REMICADE®), has been prepared through upstream construction techniques of genetic engineering, the variable region of which is still derived from murine TNF-α monoclonal antibody, maintaining the specificity and affinity binding to soluble fragments and transmembrane domains of tumor necrosis factor (Ka=1010 M−1), and the constant region of which is replaced by the human IgG1 constant region, extending the in vivo half life considerably. Other TNF-α inhibitors that have been approved for marketing abroad include an antibody fusion protein (etanercept; ENBREL®, Amgen) and a fully human anti-tumor necrosis factor-α monoclonal antibody (adalimumab; HUMIRA®, Abbott).
From the standpoints of target and specificity of action, these drugs mentioned above have almost the same mechanism of action, but all the above antibodies and fusion protein have varying degrees of problems such as high immunogenicity, low specificity and deficient stability. Therefore, there is an urgent need to establish an anti-TNF-α antibody that not only can maintain or increase the affinity and specificity of the antibody but also can reduce or eliminate the antibody immunogenicity, thereby further improving the safety and efficiency in clinical application.